The specific aims of this research proposal are: (1) To establish the molecular mechanism by which spontaneous reticulum cell sarcomas of SJL/J mice stimulate syngeneic leukocytes to proliferate in a mixed leukocyte tumor interaction. Proliferation will be measured by uptake of H3-thymidine. (2) To investigate the immunological relevance and signficance of the mixed leukocyte tumor interaction to in vivo immune parameters.